Signature surface glycan architecture promotes galectin-8-mediated vascular adhesion and metastatic dissemination of human melanomas

The molecular mechanisms enabling circulating melanoma cells to adhere to the vascular endothelium and disseminate systemically remain poorly defined. Prior data by our laboratory indicate that, as melanocytes progress to aggressive melanoma cells, they display signature surface glycan features defined by loss of I-branched poly-N-acetyllactosamines (poly-LacNAc) and a gain of galectin (Gal)-8-binding i-linear poly-LacNAcs. Here, we investigated how Gal-8-binding i-linear poly-LacNAcs remodeling influences melanoma metastasis. Flow cytometry and parallel-plate flow chamber assays were used to assess expression of canonical vascular endothelial (E)-selectin-binding glycans, sialyl Lewis X or A , and of E-selectin-mediated adhesion and Gal-8-binding pathways; RT-qPCR was used to evaluate glycosyltransferase expression necessary for canonical E-selectin binding glycans; and experimental metastasis xenograft assays were used to examine metastatic colonization. Data showed that human melanoma cells lacked E-selectin-binding glycans and expression of alpha1,3 fucosyltransferases essential for sialyl Lewis X or A biosynthesis, though they possessed an abundance of Gal-8-binding glycans, which supported robust Gal-8-mediated vascular endothelial adhesion under physiological blood flow conditions. Furthermore, in experimental metastasis assays designed to model metastatic colonization potential and our flow-based adhesion assays, exogenous rhGal-8 facilitated significantly more systemic dissemination of human i-linear poly-LacNAc high melanoma cells than control I-branched poly-LacNAc high melanoma cells. These findings support the hypothesis that Gal-8 can bridge vascular endothelial cells to i-linear poly-LacNAc high melanoma cells to support intravascular melanoma cell adhesion, implicating the Gal-8 - Gal-8-binding poly-LacNAc axis as a novel therapeutic target for disrupting systemic dissemination.